diff --git a/packages/web/integration-tests/tests/cookies/cookies.spec.js b/packages/web/integration-tests/tests/cookies/cookies.spec.js
index b9906ad5..10a70d9b 100644
--- a/packages/web/integration-tests/tests/cookies/cookies.spec.js
+++ b/packages/web/integration-tests/tests/cookies/cookies.spec.js
@@ -26,15 +26,18 @@ module.exports = {
     // This should create two streams of documentLoad sequences, all with the same sessionId but having
     // two scriptInstances (one from parent, one from iframe)
     const parent = await browser.globals.findSpan(span => span.name === 'documentFetch' && span.tags['location.href'].includes('cookies.ejs'));
-    await browser.assert.ok(parent.tags['splunk.rumSessionId']);
+    await browser.assert.ok(parent.tags['browser.instance.id']);
+
     await browser.assert.notEqual(parent.tags['splunk.scriptInstance'], parent.tags['splunk.rumSessionId']);
 
     const iframe = await browser.globals.findSpan(span => span.name === 'documentFetch' && span.tags['location.href'].includes('iframe.ejs'));
     await browser.assert.ok(iframe.tags['splunk.rumSessionId']);
     await browser.assert.notEqual(iframe.tags['splunk.scriptInstance'], iframe.tags['splunk.rumSessionId']);
 
-    // same session id
+    // same session id & instanceId
     await browser.assert.equal(parent.tags['splunk.rumSessionId'], iframe.tags['splunk.rumSessionId']);
+    await browser.assert.equal(parent.tags['browser.instance.id'], iframe.tags['browser.instance.id']);
+
     // but different scriptInstance
     await browser.assert.notEqual(parent.tags['splunk.scriptInstance'], iframe.tags['splunk.scriptInstance']);
 
diff --git a/packages/web/src/SplunkSpanAttributesProcessor.ts b/packages/web/src/SplunkSpanAttributesProcessor.ts
index f254f24a..95bf76d3 100644
--- a/packages/web/src/SplunkSpanAttributesProcessor.ts
+++ b/packages/web/src/SplunkSpanAttributesProcessor.ts
@@ -47,6 +47,7 @@ export class SplunkSpanAttributesProcessor implements SpanProcessor {
     span.setAttribute('location.href', location.href);
     span.setAttributes(this._globalAttributes);
     span.setAttribute('splunk.rumSessionId', getRumSessionId());
+    span.setAttribute('browser.instance.visibility_state', document.visibilityState);
   }
 
   onEnd(): void {
diff --git a/packages/web/src/index.ts b/packages/web/src/index.ts
index 0eeca9d4..c3edf503 100644
--- a/packages/web/src/index.ts
+++ b/packages/web/src/index.ts
@@ -70,6 +70,7 @@ import { SessionBasedSampler } from './SessionBasedSampler';
 import { SocketIoClientInstrumentationConfig, SplunkSocketIoClientInstrumentation } from './SplunkSocketIoClientInstrumentation';
 import { SplunkOTLPTraceExporter } from './exporters/otlp';
 import { registerGlobal, unregisterGlobal } from './global-utils';
+import { BrowserInstanceService } from './services/BrowserInstanceService';
 
 export { SplunkExporterConfig } from './exporters/common';
 export { SplunkZipkinExporter } from './exporters/zipkin';
@@ -433,6 +434,7 @@ export const SplunkRum: SplunkOtelWebType = {
       // Splunk specific attributes
       'splunk.rumVersion': VERSION,
       'splunk.scriptInstance': instanceId,
+      'browser.instance.id': BrowserInstanceService.id,
       'app': applicationName,
     };
 
diff --git a/packages/web/src/services/BrowserInstanceService.ts b/packages/web/src/services/BrowserInstanceService.ts
new file mode 100644
index 00000000..0329b6c0
--- /dev/null
+++ b/packages/web/src/services/BrowserInstanceService.ts
@@ -0,0 +1,53 @@
+/*
+Copyright 2024 Splunk Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { safelyGetSessionStorage, safelySetSessionStorage } from '../utils/storage';
+import { generateId } from '../utils';
+
+const BROWSER_INSTANCE_ID_KEY = 'browser_instance_id';
+
+/**
+ * BrowserInstanceService is responsible for generating and storing a unique ID for the tab.
+ * THe ID is stored in the session storage, so stays the same even after page reload
+ * as long as the tab stays on the same domain.
+ * This ID will be the same for all frames/context in the tab as long as they are on the same domain.
+ * Currently, this is simplified version which has this limitation:
+ *  - It does not cover the case when tab is duplicated -
+ *      browsers copy storage when duplicating tabs so the ID will be the same
+ *    To cover this case we need to implement a communication between tabs which requires asynchronous initialization.
+ *    This is not implemented yet as requires bigger refactoring.
+ */
+export class BrowserInstanceService {
+  static _id: string | undefined = undefined;
+
+  static get id(): string {
+    if(this._id) {
+      return this._id;
+    }
+
+
+    // Check if the ID is already stored in the session storage. It might be generated by another frame/context.
+    let browserInstanceId = safelyGetSessionStorage(BROWSER_INSTANCE_ID_KEY);
+    if(!browserInstanceId) {
+      browserInstanceId = generateId(64);
+      safelySetSessionStorage(BROWSER_INSTANCE_ID_KEY, browserInstanceId);
+    }
+    
+    this._id = browserInstanceId;
+
+    return this._id;
+  }
+}
\ No newline at end of file
diff --git a/packages/web/src/utils/storage.ts b/packages/web/src/utils/storage.ts
new file mode 100644
index 00000000..53914e73
--- /dev/null
+++ b/packages/web/src/utils/storage.ts
@@ -0,0 +1,37 @@
+/*
+Copyright 2024 Splunk Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export const safelyGetSessionStorage = (key: string): string | null => {
+  let value = null;
+  try {
+    value = window.sessionStorage.getItem(key);
+  } catch {
+    // sessionStorage not accessible probably user is in incognito-mode
+    // or set "Block third-party cookies" option in browser settings
+  }
+  return value;
+};
+
+export const safelySetSessionStorage = (key: string, value: string): boolean => {
+  try {
+    window.sessionStorage.setItem(key, value);
+    return true;
+  } catch {
+    // sessionStorage not accessible probably user is in incognito-mode
+    // or set "Block third-party cookies" option in browser settings
+    return false;
+  }
+};